This invention relates generally to nuclear reactors, and more particularly to control rod drive unit hydraulic control unit transponder cards.
A reactor pressure vessel (RPV) of a boiling water reactor (BWR) typically has a generally cylindrical shape and is closed at both ends, e.g., by a bottom head and a removable top head. A top guide typically is spaced above a core plate within the RPV. A core shroud, or shroud, typically surrounds the core and is supported by a shroud support structure. Particularly, the shroud has a generally cylindrical shape and surrounds both the core plate and the top guide. There is a space or annulus located between the cylindrical reactor pressure vessel and the cylindrically shaped shroud.
The reactor core is formed from a plurality of fuel elements. The fuel elements are grouped together at fixed distances from each other in a fuel bundle. A sufficient number of these fuel bundles are combined to form a reactor core capable of a self-sustaining chain reaction. Neutron-absorbing control rods are inserted into the core to control the reactivity of the core. The reactivity of the core can be adjusted by incremental insertions and withdrawals of the control rod.
Each control rod is housed within a vertical guide tube that ensures the vertical orientation and motion of the control rod. The control rod is moved using a control rod drive mechanism that is at least partially housed in a stub tube that also serves to support the base of the guide tube. A rod drive control system controls a hydraulic control unit (HCU) that causes the control rod drive mechanism to move the control rod, either inserting or withdrawing the rod from the fuel bundle. The HCU includes transponder cards that control the solenoids in the HCU.
Because the control rods are the primary means for regulating reactor output, it is essential that the control rod drives remain fully functional. Any failure of one of the transponder cards requires immediate attention of plant personnel to replace the defective electronics so that the HCU can become fully operational. In some cases, failure modes permit the transponder to energize the control rod movement circuitry and cause inadvertent incremental control rod insertion for a period of time before the control system detects the failure and stops the rod movement.
In one aspect, a transponder card for a nuclear reactor control rod drive control system is provided. The control system includes a control processor and a plurality of electrical devices operationally coupled to the control processor. The transponder card is configured to receive commands from the control processor, energize an appropriate electrical device when commanded, detect a failure in control circuitry of the transponder card, send a failure alarm, and remove power from an electrical device during a control circuitry failure event when there is no command to energize the electrical device.
In another aspect, a nuclear reactor control rod drive control system is provided. The nuclear reactor includes a plurality of control rods, and the control system includes a control processor, a control rod drive configured to be connected to a control rod, and a hydraulic control unit connected to the control rod drive. The hydraulic control unit includes at least one solenoid, at least one directional control valves, and at least one transponder card. Each solenoid is connected to one of the directional control valves, and each transponder card is operationally coupled to the control processor. Each transponder card is configured to receive commands from the control processor, energize an appropriate solenoid when commanded by the control processor, detect a failure in control circuitry of the transponder card, send a failure alarm to the control processor, and remove power from a solenoid during a control circuitry failure event when there is no command to energize said solenoid.
In another aspect, a method of controlling the movement of a control rod in a nuclear reactor core is provided. The method includes sending a command from a rod control processor to a transponder card in an hydraulic control unit, and energizing an appropriate directional control valve solenoid with an output from the transponder card. The hydraulic control unit includes a plurality of directional control valves and a plurality of solenoids. Each solenoid is connected to a directional control valve. The transponder card is configured to receive commands from the control processor, energize the appropriate solenoid when commanded by the control processor, detect a failure in control circuitry of the transponder card, send a failure alarm to the control processor, and remove power from a solenoid during a control circuitry failure event when there is no command to energize the solenoid.